AIS August 2014 : Eurasian Water Milfoil

Submersed aquatic plant with 3-4 feather like leaves arranged in a circle around the stem. Each feather-like leave has 12 or more pairs of leaflets whereas native Northern water milfoil has less than 10 pairs. Monitoring and prevention are key to controlling the spread!



  • Submersed aquatic plant
  • 3-4 feather-like leaves in circle around stem
  • Leaves are divided into 12 or more pairs of threadlike leaflets (native northern water milfoil has 10 or fewer pairs)
  • Stems may show pinkish-red color
  • 4-petaled pink flowers on a spike above water
  • Grows best in fertile, fine-textured, inorganic sediments in nutrient rich alkaline lakes
  • Prefers heavily used, highly disturbed lakes receiving nitrogen and phosphorus-laden runoff
  • High water temperatures promote multiple periods of flowering and fragmentation
  • Native to Europe, Asia, and northern Africa,arrived in WI in the 1960’s

Life History

  • Reproduces vegetatively by fragmentation and runners (stolons)
  • Produces shoot fragments 1-2 times/summer, carried downstream by water currents or boaters
  • Very poor seed germination
  • Rapid growth in spring because stolons, lower stems, and roots overwinter

Why Is It A Problem?

  • Forms dense leaf canopy shading out native aquatic plants resulting in monotypic stands
  • Disrupt predator-prey relationships by keeping out larger fish and reducing nutrient-rich native plants for waterfowl
  • Inhibits recreational uses like swimming,boating, and fishing
  • Obstruct industrial/power generation intakes
  • Cycle nutrients from sediment to water column, decreasing water quality and algae blooms
  • Can stay alive for weeks if moist

What Can Be Done?

  • Monitoring and Prevention!
  • Dispersed by boats, motors, trailers, bilges, live wells, or bait buckets
  • Check all equipment used in infested waters and remove all aquatic vegetation
  • Learn to identify and check for new colonies

Biological Control Methods

  • Eurhychiopsis lecontei, a native weevil
  • Adults feed on the stems and leaves, and females lay eggs on tip. Larvae bore into stems and cause extensive damage
  • Three generations of weevils hatch each summer, females lay up to two eggs per day

Mechanical Methods

  • All roots and fragments MUST BE removed
  • Hand-pull if <0.75 acres or <100 plants because thorough and selective
  • Mechanical cutters and harvesters are nonselective and remove beneficial aquatic plants
  • Harvesting creates fragments so only use on widespread established colonies
  • Hand cutters work best inshore
  • Bottom screens prevent new sprouts and kill grown sprouts; good for severe infestations in low boat traffic areas but are non-selective

Chemical Methods

  • Herbicide treatment not recommended because non-selective and disruptive to aquatic ecosystems

Note: DNR permits are required for chemical treatments, mechanical treatments, some manual treatments, biological control, bottom screening, and buoy/barrier placement.